In the field of optical communications, the necessity of parallel processing of a plurality of optical signals has been increasing with increasing channel capacity. Accordingly, the use of a plurality of optical fibers or opto-functional devices in the form of an array has been spreading. In particular, a fiber sheet in which an array of optical fibers is closely provided has recently been employed in many cases.
To reduce the coupling loss in optical transmission, optical fibers may be connected as follows: the optical fibers are inserted into an opening of a component called a ferrule included in an array connector, and are then fixed to the component, whereby the optical axes thereof are aligned with each other and the optical paths are arranged and maintained to be straight. In general, a fiber array is connected to an array connector as follows.
1) The sheath provided over the fiber array is removed and a portion, e.g., glass cores, of the fiber array thus exposed is cut so as to have an appropriate length. The fiber has the glass core, and the core is coated by the cover. The glass core includes a clad and a core. Hereinafter, the glass core is called a core.
2) The exposed portion of the fiber array is inserted into the opening of the ferrule and is fixed to the ferrule with adhesive.
3) The end of the fiber array projecting from an end face of the ferrule is ground and is thus aligned with the end face of the ferrule.
In a case of a fiber sheet that includes many optical-fiber transmission lines, a plurality of array connectors may be used. To perform the above grinding and alignment of fiber ends simultaneously or individually on different array connectors, optical fibers having excessive lengths need to be appropriately processed. This problematically reduces the working efficiency.
To solve such a problem, there has already been proposed an optical connector, i.e., an array connector, (see Japanese Unexamined Patent Application Publication No. 2006-145787, for example) that includes two separable portions: a portion (rear block) into which optical fibers are to be inserted, and a portion (front block) for making optical connection. In this case, the grinding and alignment of fiber ends only needs to be performed on the front block separated from the rear block, and variations in the lengths of the optical fibers projecting from the rear block are absorbed by a refractive-index-matching film interposed between the front block and the rear block.
The refractive-index-matching film is, for example, a transparent, elastic, gel-type film. The optical fibers projecting from the contact surface of the rear block are embedded into the refractive-index-matching film while elastically deforming the film, whereby the projecting portions of the optical fibers are absorbed. Hence, there is no need to grind the ends of the optical fibers projecting from the rear block, and the grinding and alignment of fiber ends is performed only on the front block. In the grinding and alignment of fiber ends performed on the front block, there is no need to process optical fibers having excessive lengths, and the working efficiency is improved. Instead, however, the grinding needs to be performed on both sides of the front block. This leads to another problem of an increase in the assembling cost.
To solve such a problem, there has already been proposed a technique (see Japanese Unexamined Patent Application Publication No. 2001-215364, for example) in which fibers of a fiber array are held by a holding member and the ends of the fibers having various lengths are pressed against a collimating optical system whose entrance surface is fixed, so that no gaps are provided between the optical system and the fibers. In this case, the fibers are slightly bent when the ends thereof are pressed against the collimating optical system. Thus, the variations in the lengths of the fibers (variations in the positions of the ends of the fibers) are absorbed.
The range of variations in the projecting lengths of optical fibers that can be absorbed by interposing a refractive-index-matching film between the front block and the rear block as described above is several microns at most. If the fibers attached to the rear block project by different lengths varying over a range larger than several microns, such variations cannot be absorbed by the refractive-index-matching film. In some cases, the range of variations in the projecting lengths of optical fibers is larger than several microns, and the variations cannot be completely absorbed with the refractive-index-matching film alone. Accordingly, the grinding and alignment of fiber ends may be necessary for the rear block in some cases.
The range of variations in the projecting lengths of optical fibers that can be absorbed by bends in the optical fibers that are pressed against the collimating optical system as described above is also several microns at most, and the variations cannot completely be absorbed by this method, either. That is, the grinding and alignment of fiber ends may be necessary in some cases.